Electrical apparatus and insulating bushing therefor



Jan. 24, 1933. G. E. JANSSON ELECTRICAL APPARATUS AND INSULATING BUSHING THEREFOR Filed March 30. 1928 20 jfivehiarj all) Patented Jan. 24, 1933 UNITED STATES PATENT OFFICE GUSTAV E. JANSSON, OF WOLLASTON, MASSACHUSETTS, ASSIGNOR TO CONDIT ELEC- TRICAL MANUFACTURING CORPORATION, OF SOUTH BOSTON, MASSACHUSETTS, A

CORPORATION OF MASSACHUSETTS ELECTRICAL APPARATUS AND INSUILATING BUSHING THEREFOR Application filed March 80, 1928. Serial No. 266,084.

This invention relates to high tension electrical apparatus and insulating bushings for the terminals thereof and to means for deriving a small amount of power from the high tension circuit of the apparatus by the capacity current through the insulating bushing for the operation of synchronizing indicators, volt meters, and the like. In my c0- pending application Serial No. 248,238, filed January 20, 1928, I have shown an arrangement of bushing for this purpose. The bushing is of the oil filled type having a metal flange or collar which provides the attach ing means and the support for the bushing, the collar'being spaced and insulated from the casing to which it is attached and thus constituting an intermediate terminal of a condenser of which the high tension terminal of the bushing is the high tension plate and the casing is the low tension plate.

The current through such apparatus is dependent upon the capacity between the easing and the collar, and between the collar and the high tension conductor, which capacities are in series. The potential of the collar is dependent upon the ca acity between the collar and the casing. 11 some instances the capacity between the collar and the casing is so low that the collar has a potential that is too high for convenient use in indicating apparatus.

It is an object of this invention to provide a bushing and easing construction arranged as above set forth wherein a separate condenser is associated with the casing and bushing and is connected between the bushing collar and the casing. With this arrangement, the separate condenser can have any desirable capacity and can thus bring down the voltage of the collar to a selected value.

it is also an object of this invention to support the collar of the bushing from the casing lay insulating means in such a manner that the direct capacity between the collar and the bushing is reduced as much as practicable so that the voltage oi the bushing collar will be governed practically entirely by the separate condenser and will not be appreciably afiected by conditions that may arp in difi'erent pieces of apparatus.

To this end, it is a further object of the present invention to support the bushin collar from and in spaced relation with the casing by insulating means having a low specific inductive capacity and to use but a small amount if solid dielectric.

A further object of the invention is generally to improve the construction of insulating bushings.

Fig. 1 is an elevation partly in section of an insulating bushing applied to an electric switch.

Fig. 2 is a diagram of the circuit connections between the condenser elements of the bushing and an indicating apparatus.

As here shown the bushing comprises a metal tube or sleeve 10 which has an annular flange 12 at the upper end in which the porcelain shell 14 is received. The lower end of said sleeve is provided with an enlarged annular flange 16 in which. a lower porcelain shell 18 is received.

The high tension conductor or stud 20 is extended axially through said shells and is provided at the lower end with a contact member 22 which cooperates with a movable switch member 24 to close the circuit through the switch. The bushing is adapted to be oil filled to insulate the stud 20 from the metal tube 10.

The invention may be applied to any suitable type of high tension bushing having the metal tube 10 or the equivalent carried by it and which forms means for supporting the bushing on the casing of the electrical apparatus.

The bushing, as here shown, is inserted through an opening 26 in the casing 28 of the switch and the lower end of the tube 10 is adapted to be immersed beneath the oil in the casing. The tube 10 at its upper end is provided with a radially outstanding attaching flange 30 which is formed with a pair of radially spaced concentric grooves 32 in its lower face. The casing 28 is formed with a similar set of grooves 34: which are opposed to the grooves 32. Short sections of insu lating tubes or rings 36 are received in said opposed sets of grooves and as and thus suitable to provide the desired spacing be-' tween the flange 30 and the casing. Bolts 38 pass through the flange and are screw l threaded into the casing to secure the bushing and the tubes 36 in the aforesaid relation.

The bolts are insulated from the flange by insulating tubes 40 and washers 42, and

thebolt-passages through the flange are preferably enlarged as at 44 to reduce the capacity between the bolts and the flanges as much as is practicable.

With this arrangement the greater proportion of the entire space between the flange 30 and the casing is filled with air which has a low specific inductive capacity. While the specific inductive capacity of the material composing the rings 36 is greater than that of air, the amount of material is small and the length is long so that the increased capacity provided by the material is negligible. Consequently the capacity between the flange 30 and the casing is small.

In accordance with this invention, a condenser 46 is connected between the casing and the flange of the bushing. The condensor can be of any suitable construction. As

here shown, it consists of a metal enclosing shell which forms one terminal of the condenser and contains and encloses the elements of the condenser. The condenser is rovided with an insulating bushing 48 having a terminal 50 at the upper end thereof which is connected to the condenser elements within the shell.

The metal shell of the condenser is attached to the lower end of and is electrically connected to the supporting bracket 52, the upper end of which is attached to the face of the casing 28. The condenser preferably depends below the levelof oil in the casing and is adjacent the bushing. A lead 54 is connected to the high tension terminal 50 of the condenser and extends through a bushing 56 in the casing 28 and is electrically connected with the terminal 57 of the flange 30. Thus, the condenser is shunted between the flange and the casing. The insulated flange 30 is protected from the weather by a housing 58 of any suitable construction which may be as shown in my above named application.

A lead 60 extends from the flanged terminal 57 through an insulating bushing 62 of the housing and is connected with one terminal of a suitable measuring device 64, the other terminal of which is connected to the casing 28 and the terminal 66 thereof. The casing usually is grounded.

With the arrangement shown, the capacity of the condenser 46 can be made much greater than any capacity which can reasonably be obtained by the interposition of a dielectric between the flange 30 and the casing 28 so that the capacity current and the power transmitted through the bushing can be increased and the potential of the flange 30 can be reduced to a satisfactory value. The capacity of the condenser 46 is much greater than the capacity between the flange 30 and casing 28 so that the latter capacity is negligible in influencing the potential of the flange. Thus the potential, or the reading of the device 64, is independent of any variations in capacity between the flange and casing as might occur due to atmospheric variations and variations in assembly procedure.

I claim:

1. The combination of the oil-containing casing of an electric apparatus and a high tension bushing therefor extended into the oil in and insulated from said casing and having an attaching flange carried by and insulated from said casing constituting a low tension condenser terminal, said casing and flange constituting a low capacity condenser and a high capacity condenser carried by said casing internally thereof, and immersed in the oil therein and having its terminals connected with said casing and said attaching flange.

2. The combination of a support, and an insulating bushing extended through said support and having an external outstanding flange overlying said support, a spacing tube of insulating material surrounding said bushing and interposed between said flange and support, said tube being thin as compared with the extent of said flange, and means to clamp said flange on said tube.

3. The combination of a support, an insulating bushing extended through said support and having an outstanding flange which overlies and is spaced from said support, the confronting faces of said support and flange having concentric spaced and opposed annular grooves therein, said tubes aving small cross-sectional area as compared with the area of said flange, radiallyspaced spacer tubes of insulating material received in said opposed grooves of said flange and support and surrounding said bushing, and insulated clamping means connecting said flange and casing and holding said flange upon said tubes.

4. The combination of a support, an insulating bushing having an outstanding flange, the confronting faces of said support and flange having concentric spaced and opposed annular grooves therein, spacer tubes of insulating material received in said opposed grooves of said flange and support, said tubes aving a small cross-sectional area as compared with the area of said flange, the space between said flange and casin otherwise containing air so that the speci c inductive capacity of the dielectric medium in said space is in eflect that of air, and insulated clamping means connecting said flange and support 10- cated in the space between said tubes.

5. A voltage-transforming apparatus comprising the combination of a grounded support, a high tension bushing carried thereby having an attaching flange, insulating means which spaces said flange and support and interposes a dielectric medium therebetween that has a specific inductive capacity approximately equal to unity, so that the capacity between said support and flange is kept down to a low value, and a condenser connected between said support and flange having a capacity which is much greater than the capacity between said flange and support so that said latter capacity has a negligible influence on the potential of said flange.

6. The combination of a grounded support, a high tension insulating bushing extended through said support and having an outstanding attaching flange that is spaced from said support, said flange and sup ort constituting a condenser of which said flange constitutes a terminal that is at a higher potential than said support, and means to keep down the capacity between said flange and support comprising insulating supporting members located between and spacing said flangeand support apart, said members occupying but such a small part of the space between the flange and support, which space otherwise contains air, that the specific inductive capacity of the total dielectric medium in said space is practically that of air.

7. The combination of a grounded support, a high tension insulating bushing extended through said support and having an outstanding attaching flange that is spaced from said support, said flange and support constituting a condenser of which said flange constitutes a terminal that is at a higher potential than said support, and means to keep down the capacity between said flange and support comprising insulating supporting members located between and spacing said flange and support apart, said members occupying but such a small part of the space between the flange and support, which space otherwise contains air, that the specific inductive capacity of the total dielectric medium in said space is practically that of air, and a condenser connected between said flange and support having a capacity that is so much greater than that of said flange and support that said latter capacity has a negligible influence on the potential of said flange,

in testimony whereof, I have signed my name to this specification.

GUSTAV E. JANSSON. 

